THE RESPONSE OF LONGAN FRUIT TO COLD AND GAMMA-IRRADIATION TREATMENTSFOR QUARANTINE ERADICATION OF EXOTIC PESTS

In separate treatments. fruit of Dimocarpus longan Lour. were subjecte d to 15 d at 1.1 degrees C or to gamma irradiation from Co-60 source. Cold-treated fruit were not significantly different from untreated fru it in characteristics including decay susceptibility, firmness, and th e percentage of total soluble solids and acids in the pulp, but treatm ent produced patches of bronze discolouration on the pericarp. Gamma i rradiation at 100, 200, or 300 Gy did not significantly affect suscept ibility to decay or injure fruit, nor were firmness or external and in terior colour reduced. Irradiated fruit, however, had lower percentage s of total soluble solids and acids, with a concomitantly higher pH, b ut sensory evaluations could not differentiate these fruits from untre ated ones. Due primarily to the injurious effects of cold treatment on the longan pericarp, irradiation at 100 to 300 Gy would be preferable for maintaining quality of longans that require quarantine treatment for the eradication of exotic pests and are destined for the fresh mar ket.